Recently, the need for a high voltage comparator or an operational amplifier with a wide adjustable threshold range is growing in electronic industry. This is because in various applications, such as automotive application, a battery voltage is always very high, for example 40V. Besides, such a chip is extremely required, which could monitor the currents of different types of external high voltage MOS transistors via their drain to source voltages. The drain to source voltages of the high voltage MOS transistors are usually above 3.3V. Therefore, how a comparator or an operational amplifier could operate properly and accurately with high input and reference voltages is extremely important.
In one possible solution in the prior art, a divider is applied in order to set the input and reference voltage into a typical CMOS operable range. However, for example, the divider may amplify the random offset noise within the comparator or the operational amplifier, which is severe when the input voltage is close to 0V. Also, a voltage level shift is not possible in the above solution.